Watercraft are often powered by an inboard or outboard motor. The motor includes a water propulsion device, such as a propeller, which is powered by an internal combustion engine. The engine has an output shaft which drives the water propulsion device.
Normally, the engine drives the propeller via a transmission. The transmission permits the engine to drive the propeller in reverse and forward directions, or not at all when in a neutral position. The transmission includes a clutch which permits shifting between the various drive positions.
Fuel is supplied to the engine with a fuel system. In one arrangement, fuel is supplied to air passing through an intake pipe with a carburetor. The operator of the watercraft controls the speed of the engine with a throttle control. The throttle control controls both the carburetor and a throttle valve, thereby controlling the fuel supply rate and air flow rate. In this manner, the operator controls the speed of the engine.
As is well known in this arrangement, when the operator rapidly closes the throttle valve when the engine speed is relatively high, the air flow rate decreases faster than the engine speed. Until the engine speed drops, the pumping action of the engine may draw fuel from the carburetor. This excessive fuel delivery may cause engine backfire and foul any exhaust catalyst associated with the engine.
To reduce this problem, the throttle control includes a damping or delay member, such as a pneumatic cylinder. This damping member prevents the throttle valve too rapidly in relation to movement of the throttle control by the operator.
FIG. 9 illustrates the relationship between throttle control movement and engine speed in this arrangement. Line 1 represents throttle angle (as controlled by the throttle control), while line 2 represents ideal engine speed. The tine .DELTA.Td represents the time during which changes in engine speed are delayed in relation to the movement of the throttle control. This arrangement has the benefit that the engine speed is reduced gradually even when the throttle control is closed quickly, reducing the probability of the engine drawing excessive fuel from the carburetor.
A detriment to this arrangement, however, is that no matter how fast the operator closes the throttle valve, the engine speed will only reduce to idle at a gradual rate. If the engine speed has not reduced sufficiently between the time the operator closes the throttle valve and when the transmission is shifted, the transmission may engage or disengage harshly. This is a common problem when the throttle control and shift lever are integrated into the same control.
As one attempt to remedy this problem, the timing of the start of the damping or delay mechanism may be advanced, as illustrated by line 3 in FIG. 9. This arrangement has the problem that the engine speed does not reduce as desired. On the other hand, if the timing of the damping mechanism is delayed, the engine speed may fall below the desired speed, as illustrated by line 4 in FIG. 9. This might result in stalling of the engine or the like.
An engine control is desired which overcomes the above-stated problems.